SPORTING LISBON have targeted Dundee United ace Stuart Armstrong and are expected to challenge Celtic to sign the midfielder, according to reports in Portugal.

SPORTING LISBON have targeted Dundee United ace Stuart Armstrong and are expected to challenge Celtic to sign the midfielder, according to reports in Portugal.

Celtic have pinpointed the 22-year-old as part of a January transfer window recruitment drive.

However, Portuguese giants Sporting are now a serious obstacle to their hopes of landing Armstrong, after their scouts watched him recently.

Sporting have already raided United this season of course to sign precocious talent Ryan Gauld on a six-year deal that included a £48m buy-out clause.

They have been impressed by Armstrong, his fellow Scotland Under-21, after a series of impressive showings this term.

United are under no pressure to sell having also sold Andrew Robertson to Hull City.

But Armstrong would be interested in hearing what Sporting had to offer.

Sporting are keen to add some new faces after yet another disappointing campaign that has left them languishing in fourth place.

They are desperate for success having not won a domestic trophy since 2008.